Identical and Still Different

Even in monozygotic twins reared together, there are always observable differences reflecting the influence of individual responses. Freund et al. (p. 756; see the Perspective by Bergmann and Frisén) developed an inbred mouse model for studying the environmental influences on genetically identical animals and examined their effects on behavioral and neural development.

Abstract

Brain plasticity as a neurobiological reflection of individuality is difficult to capture in animal models. Inspired by behavioral-genetic investigations of human monozygotic twins reared together, we obtained dense longitudinal activity data on 40 inbred mice living in one large enriched environment. The exploratory activity of the mice diverged over time, resulting in increasing individual differences with advancing age. Individual differences in cumulative roaming entropy, indicating the active coverage of territory, correlated positively with individual differences in adult hippocampal neurogenesis. Our results show that factors unfolding or emerging during development contribute to individual differences in structural brain plasticity and behavior. The paradigm introduced here serves as an animal model for identifying mechanisms of plasticity underlying nonshared environmental contributions to individual differences in behavior.